The invention relates to a method for adjusting and changing the height of the plane of passage of a material rolling through rolls of consecutively arranged rolling stands of a shape rolling mill, which stands include a flange upsetting stand arranged between two universal rolling stands. These adjustments are performed by raising or lowering the rolling stands and/or parts of the rolling stands supporting the rolls, as well as apparatus for performing the method.
The rolling of structural parts, especially girders or beams in shape rolling mills requires an accurate as possible observation of the inlet and outlet of the material to be rolled into the rolling gap at a right angle to the common roll axis plane of the top and bottom roll. This applies especially to universal rolling of girders having parallel flanges, since a deviation from these inlet conditions can change the position of the web center with respect to the rolling plane and thus cause a web mismatch impairing the quality of the finished product.
In universal rolling stands, one rolling gap is formed between the horizontal rolls and one rolling gap on each side of the respective vertical roll and the side flanks of the horizontal rolls facing the vertical roll. In case of an entry which is not at right angles, the girder section is constrained to climb into the rolling gap and is then raised by the bottom roll. The girder is aligned in the rolling gap and falls after its exit from the rolling gap approximately into the same height position corresponding to its entry. Herein the vertical rolls rotate around their vertical axes and cause, from the start of the deformation, an alignment of the material to be rolled into the mentioned position at right angles, meaning there occurs bending of the girder, which builds up the longitudinal stresses across the crosssection, which are felt in the lower flange halves as compressive stresses and in the upper flange halves as tensile stresses. The compressive stresses favor the lateral spread with thickness reduction of the flange, while the tensile stresses hinder the same, with the result that the lower flange halves widen more and the upper flange halves less or not at all. This different widening of the upper and lower flange halves leads to the quality impairing web mismatch.
In order to do away with these disadvantageous consequences of the rolling process, it has already been proposed to lift or lower the roll stand by means of shimstocks introduced between stands and base plates or also intermediate base plates and thus to assure a rectangular or correct entry angle for the material to be rolled. It is also known to use lifting devices placed beneath the stand instead of shimstock or (EP-patent application 88106436.4) to arrange the universal roll set consisting of a pair of horizontal rolls and a pair of vertical rolls so as to be vertically movable and positionally fixable within the universal rolling stand which is arranged to be stationary.
The described adaptations of the stand heights are performed prior to starting the rolling operation and are possibly corrected after rolling samples have passed through the stands. This requires considerable time expenditures and consequent down times of the rolling train. It has been shown to be particularly disadvantageous in that one experiences, for instance, a web center mismatch frequently during the rolling operation caused by change in the condition of the preliminary product, which makes it necessary to again stop the rolling train in order to perform the required corrections of the height position of the rolling stands.